docs: def get_paths(rlz):
      """
      :param rlz:
          a logic tree realization (composite or simple)
      :returns:
          a dict {'source_model_tree_path': string, 'gsim_tree_path': string}
      """
      dic = {}
      if hasattr(rlz, 'sm_lt_path'):  # composite realization
          dic['source_model_tree_path'] = '_'.join(rlz.sm_lt_path)
          dic['gsim_tree_path'] = '_'.join(rlz.gsim_lt_path)
      else:  # simple GSIM realization
          dic['source_model_tree_path'] = ''
          dic['gsim_tree_path'] = '_'.join(rlz.lt_path)
      return dic